The present invention relates to a receiver for a code division multiple access (CDMA) system in which individual users have various transfer rates. The present invention generally belongs to digital interference noise filtering technology. Conventional technologies include a serial interference canceller, parallel interference canceller and a hybrid interference canceller. The present invention is concerned with the parallel interference canceller among the conventional technologies. In particular, the present invention is concerned with a parallel interference canceller in an asynchronous CDMA receiver having multiple transfer rates.
Representative conventional technologies relating to the interference canceller have been developed by Virginia Technology Institute of the United States and ETRI of Korea. First, ETRI proposed a technique for canceling interference in a block unit by collecting bits or symbols. This technique has a problem that the capacity of a memory buffer has to be increased to implement the system. Particularly, as this technique employs a method of checking asynchronously overlapped portions more than once, there is a problem that the accuracy of detection at the overlapped portions is lowered.
Meanwhile, Virginia Technology Institute proposed a sequential interference cancellation scheme. In this scheme, however, the calculation process for detecting and reproducing signals, the signal reduction process and the de-spreading process for restoring original signals from which interference is canceled are not arranged in order but mixed. Thus, the calculation contents and the object data differ for each bit of calculation. Therefore, this method requires much load of control processing in addition to data calculation. Thus, when this method is implemented in hardware, it is difficult to improve the processing speed and control of the processing flow is complicated.